1. Field of the Invention
The present invention relates to a semiconductor memory with a resistance change element, and is used for a magnetic random access memory (MRAM).
2. Description of the Related Art
In recent years, development race for universal semiconductor memory has become active, the semiconductor memory advantageously having features of high speed, high integration, low power consumption and high reliability despite its non-volatility. One of them is a magnetic random access memory utilizing a magneto-resistive effect (for example, refer to “16 Mb MRAM Featuring Bootstrap Write Driver” 2004 Symposium on VLSI Circuits Digest of Technical Paper, pp. 455-457).
A memory cell of the magnetic random access memory is comprised of, for instance, a magnetic tunnel junction (MTJ) element as a resistance change element; and the MTJ element has a fundamental structure of a layered structure comprising a magnetic pinned layer, a magnetic free layer and a tunnel barrier layer existing therebetween.
In such a MTJ element, when the magnetization direction of the magnetic pinned layer is the same as that of the magnetic free layer, tunnel probability of the tunnel barrier layer becomes maximum, resulting in a minimum resistance value of the MTJ element. This state is defined as a parallel state which is caused to correspond to, for instance, “0”.
Further, when the magnetization direction of the magnetic pinned layer is opposite to the magnetization direction of the magnetic free layer, tunnel probability of the tunnel barrier layer becomes minimum, resulting in a maximum resistance value of the MTJ element. This state is defined as an anti-parallel state which is caused to correspond to, for instance, “1”.
Then, writing of data is carried out in such a way that, for instance, magnetization state of the MTJ elements is controlled while utilizing a magnetic field (current magnetic field) generated due to a write current, or a spin polarized electron generated by flowing spin injection current into the MTJ element, or the like. Further, read of data is carried out by flowing read current into the MTJ element and detecting its resistance value.
One of the problems to be solved, when the universal semiconductor memory represented by the above-described magnetic random access memory is put into practical use, is reduction of power consumption.